Not much time has passed since the Horde and Alliance joined sides to repel the invaders of the World Tree Nordrassil, due to these events it has not been enough time for humans and night elves to mingle. This does not mean half-night elves do exist, as their a probably a few less half-night elves then half elves. This race resembles humans far more than night elves, half-night elf birth is rare but most follow druidism and gain their spells from the power of nature. Half-night elves are able to Shadowmeld, the night elven ability known at birth and learned from their heritage. An adult half-night elves would have been born by the primitive human race, the azotha. However, the azotha status remains unknown and it's presumed they were either killed off or either "laying low".
They can speak Darnassian and Common just like the night elves. While traveling this half-breed may learn many new languages.